During labor and childbirth, a number of physiological conditions of mother and infant typically are monitored by the attending obstetrician to determine precisely when and how the infant is to be delivered. Among the most important of these conditions are the magnitude and rate of cervical dilatation, the extent to which the cervical walls have thinned or effaced and the rate of such effacement, and the longitudinal position or station of the baby's head within the birth canal. Obviously, the reliability and accuracy of the determination of these factors can be very important since the critical decisions of when to deliver the infant and whether or not to deliver the infant by cesarian section are commonly made based on such determinations.
While medical science has made great strides in recent decades, very little progress has been made in methods of determining and monitoring the conditions of the cervix and the station of an infant's head during labor. Generally, these factors are still determined as they have been for decades through manual insertion of the doctor's or nurse's fingers through the vagina for physical examination and estimation of the condition of the cervix and infant. This method, however, has long been plagued with persistent inherent problems that can and sometimes do result in untimely delivery of the infant and can even result in the performance of unnecessary cesarian sections. These problems persist largely because the accuracy and reliability of estimates based on physical examinations are highly dependent upon the experience or even the finger size of the attending doctor or nurse. Widely varying estimates of dilatation, effacement, and station can thus be obtained depending upon who conducts the examination. This problem is often exacerbated where two or even more attendants conduct cervical examinations in the course of labor to establish dilatation and effacement rates since the resulting Friedman curves, upon which many decisions and prognoses of labor related problems are based, become virtually meaningless. It can thus be seen that an almost total lack of objectivity and standardization exists among obstetricians and obstetric attendants in the determination and monitoring of the conditions of the cervix and station of the baby during labor.
Additional problems and shortcomings inherent in prior art manual examinations include the greatly increased risk of uterine or vaginal contamination and infection that can result from repeated examination, discomfort to the mother, risk of injury to the infant through breakage of fetal membranes, and the accidental dislodging of fetal monitors that are often secured to the baby's head to monitor fetal heartbeat.
In recent years, the techniques of ultrasonographic examination of the body's internal organs without physical intrusion into the body cavity has found widespread application in the medical community including the disciplines of obstetrics and gynecology. Indeed, ultrasound examinations have proven invaluable in the diagnosis of abnormal conditions of the cervix during pregnancy such as, for example, cervical incompetence.
Ultrasound examinations of the cervix and female reproductive system are traditionally carried out using the filled bladder method described by Sarti, et al.sup.1 wherein the patient's bladder is at least partially filled with a saline solution causing it to enlarge and conform to the shape of surrounding uterine and cervical tissue. The difference in sonic density between the saline solution and surrounding tissue, then, renders the cervical outline clearly visible on an ultrasound image such that diagnosis and prognosis can easily be made. FNT .sup.1 Sarti D A, Sample W F, Hobel C J, Staisch K J, Ultrasound Visualization of a Dilated Cervix During Pregnancy, Radiology 1979; 13:417.
Unfortunately, ultrasound techniques that have become successful in diagnosing abnormal conditions of the uterus during pregnancy have not, as a general rule, proven themselves useful in monitoring the conditions of the cervix and station of the fetal head during labor itself. This is due in part to the thinning of the cervical tissue during labor and to the substantially homogenous sonic density of the cervix and surrounding tissue, all of which renders the cervix and the relationship of the fetal head thereto indistinct in ultrasound images. Further, the filled bladder method of visualizing the cervix in the course of pregnancy is generally inapplicable during labor since the pressure of the inflating fluid within the bladder can deform the uterus and cervix and interfere with normal delivery of the infant. As a consequence, traditional manual examinations with their attendant inaccuracies, problems, and risks continue to be employed by obstetricians throughout the world for monitoring the progress of labor.
Thus, it is seen that a continuing and heretofore unaddressed need persists for a method of examining the cervix ultrasonically during labor and of monitoring the progress of its dilatation and effacement. Such a method should provide objective standardized and accurate indications of the cervical condition as well as the station of the infant's head with a minimum of physical intrusion and risks to mother and infant. It is to the provision of such a method and an apparatus for facilitating performance thereof that the present invention is primarily directed.